1. Field of the Invention
The present invention relates to a toner amount detecting apparatus for detecting a toner residual quantity (amount) and an integrated quantity of disposal toner in an image forming apparatus such as a copying machine, a printer and a facsimile etc. which utilize an electrophotographic processing system.
2. Related Background Art
FIG. 10 is a view schematically showing a construction of an image forming apparatus (which is a laser beam printer of a full-color mode) utilizing an electrophotographic processing system.
This image forming apparatus is constructed of an apparatus body (a printer engine) 19 incorporating a drum-like photographic photosensitive body (which is hereinafter referred to as a photosensitive drum) 1, a charging roller 2, an exposure apparatus (a scanner apparatus) 3, a developing apparatus 4, an intermediate transfer belt 5 serving as an intermediate transfer member, a secondary transfer roller 7, a conveying guide member 8, and a fixing unit 9.
The photosensitive drum 1 has an organic photoconductive layer (not shown) formed on a drum substrate (unillustrated) composed of aluminum. The photosensitive drum 1, to which a driving motor (not shown) is connected, rotates at a predetermined process speed by the driving motor.
The charging roller 2 is pressed by a predetermined pressing force against the surface of the photosensitive drum 1, and is so driven as to rotate with a rotational drive of the photosensitive drum 1. A power source (not shown) applies a predetermined charging bias to the charging roller 2, and the photosensitive drum 1 is thus subjected to a charging process with a predetermined polarity at a predetermined electric potential.
The exposure apparatus (the scanner apparatus) 3 includes an unillustrated laser diode, a polygon mirror, an image-forming lens system, and a reflecting mirror 3a. Upon an input of an image signal, the laser diode irradiates the polygon mirror with a beam of image light corresponding to the image signal. The surface of the photosensitive drum 1 rotating at a fixed speed is selectively exposed to the beam of image light reflected by the polygon mirror rotating at a high speed, thereby forming an electrostatic latent image on the surface of the photosensitive drum 1.
The developing apparatus 4 includes a yellow developing unit 4Y, a magenta developing unit 4M, a cyan developing unit 4C and a black developing unit 4Bk which serve to turn the electrostatic latent image into a visible image. The yellow, magenta, cyan and black developing units 4Y, 4M, 4C and 4Bk are provided with sleeves 4Ys, 4Ms, 4Cs and 4Bks, respectively.
The yellow, magenta, cyan and black developing units 4Y, 4M, 4C and 4Bk rotate with rotations of a developing rotary unit 4A when forming the image, and a predetermined sleeves among the sleeves 4Ys, 4Ms, 4Cs and 4Bks faces at a spacing as minute as approximately 300 .mu.m to the photosensitive drum 1. A predetermined developing unit among the yellow, magenta, cyan and black developing units 4Y, 4M, 4C and 4Bk thereby halts in a developing position facing to the photosensitive drum 1, whereby the visible image is formed on the photosensitive drum 1.
The intermediate transfer belt 5 is supported by a drive roller 5a, a secondary transfer face-to-face roller 5b and a tension roller 5c, thus keeping a proper tension. The primary transfer roller 6 is so disposed as to come into contact with the photosensitive drum 1 through the intermediate transfer belt 5.
Next, an image forming operation by the image forming apparatus described above will be explained.
When forming the image, an unillustrated outside host computer outputs a print request signal to a printer engine controller. Next, after starting up a scanner motor (not shown), a start-of-print preparing operation is executed within the apparatus body 19, corresponding to the print signal. Upon a standby status, the printing operation is started.
A transfer material P such as a sheet of paper is fed out of a cassette paper feeding portion 10 by a cassette paper feed roller 11 or out of a multi-manual paper feeding portion 12 by a multi-manual paper feed roller 13, and is carried by a carrier roller 14. Then, the transfer sheet P, of which a skew feeding is corrected by a resist roller 16, thereafter temporarily stops. Hereupon, a timing is adjusted so that a front edge of the transfer sheet P is coincident with a front edge of the image, and the transfer sheet P is again carried.
On the other hand, the photosensitive drum 1 is rotationally driven by the driving unit (unillustrated) at the predetermined process speed, and receives the charging process with a predetermined polarity at a predetermined electric potential by the charging roller 2 to which a predetermined charging bias is applied. Then, the surface of the thus charged photosensitive drum 1 is image-exposed by the laser beams of the exposure apparatus 3, thereby forming an electrostatic latent image corresponding to a first color component image (e.g., a yellow component image) of a desired color image. Then, this electrostatic latent image is developed with the yellow toner defined as a first color by the yellow developing unit 4Y.
The first-color yellow toner image formed and borne on the photosensitive drum 1 is, in the process of passing through a transfer nip (a primary transfer portion) between the photosensitive drum 1 and the intermediate transfer belt 5, primarily transferred onto the intermediate transfer belt 5 by a pressure given at the primary transfer roller 6 and by a primary transfer bias applied to the primary transfer roller 6. Hereinafter, a second-color magenta toner image, a third-color cyan toner image and a fourth-color black toner image which are similarly formed and borne on the photosensitive drum 1 by the magenta developing unit 4M, the cyan developing unit 4C and the black developing unit 4Bk, are sequentially transferred in superposition onto the intermediate transfer belt 5, thus forming a synthetic color toner image corresponding to the desired color image.
Then, the transfer sheet P is fed at the timing described above to the transfer nip (the secondary transfer portion) between the intermediate transfer belt 5 and the secondary transfer roller 7. On this occasion, a secondary transfer bias is applied to the secondary transfer roller 7, and the synthetic color toner image is transferred onto the transfer sheet P from the intermediate transfer belt 5.
The transfer sheet P, onto which the synthetic color toner image has been transferred, is conveyed to a fixing unit 9 by the conveying guide member 8, and the color visible image is permanently fixed onto the transfer sheet P with heating and pressurization by a fixing roller 9a and by a pressurizing roller 9b. This transfer sheet P is discharged onto a discharge tray 18 via pairs of discharge rollers 17a, 17b, 17c.
The main body 19 of the image forming apparatus described above is provided with a toner residual quantity detecting apparatus for detecting a residual quantity of each color toner (the yellow toner, the magenta toner, the cyan toner and the black toner) used for the developing apparatus 4.
FIG. 11 is a view showing a construction of a light transmission type toner residual quantity detecting apparatus by way of one example thereof. This toner residual quantity detecting apparatus is provided on a side surface of the main body 19 of the apparatus in close proximity to a toner cartridge (toner CRG) 23 of the developing apparatus 4.
Referring to FIG. 11, a unit 21 is mounted with a light emitting element 20 and a light receiving element 22, and light guides 25, 26 serve to guide a quantity of light emitted from the light emitting element 20 to the light receiving element 22 via windows 24a, 24b of the toner CRG 23.
In this toner residual quantity detecting apparatus, a beam of light A emitted from the light emitting element 20 is incident upon the window 24a of the toner CRG 23 through within the light guide 25. Then, an agitator plate (see FIGS. 12A and 12B) 27 provided inside the toner CRG 23 scrapes off the toner T in the vicinity of the window 24a, whereby the incident light A travels through inside the toner CRG 23 and emerges from the window 24b. The light A having emerged therefrom is received by the light receiving element 22 via the light guide 26.
On this occasion, a detection timing of the light receiving signal is defined by a time width till the toner is agitated in the toner CRG 23 and consequently again covers over the vicinity of the window 24b enough to make the light A enable to penetrate, based on a point of time when the light A having passed through starts falling upon the light receiving element 22. This time signal pulse width differs depending on the toners left in the toner CRG. Accordingly, the toner residual quantity is judged based on this pulse width time signal.
Namely, as illustrated in FIG. 12A, if the toner residual quantity is large, the vicinity of the window 24b is covered with the toner T even when agitated by the agitator plate 27, and hence the time width of the pulse width signal decreases. Further, as shown in FIG. 12B, if the toner residual quantity is small, the vicinity of the window 24b is covered with a small quantity of the toner T, and therefore the time width of the pulse width signal increases.
FIG. 13 is a diagram showing a relationship between a light emission timing of the light emitting element 20, the light receiving signal of the light receiving element 22 which corresponds to a degree of the toner residual quantity, and a detection sampling timing of the light receiving signal.
Referring to FIG. 13, a level 1 of the light receiving signal indicates that the toner residual quantity is large, while a level 3 of the light receiving signal indicates that the toner residual quantity is small. Further, a level 2 of the light receiving signal indicates a toner residual quantity intermediate between the level 1 and the level 3. The light receiving signal is detected based on the pulse time width sampled during a light emitting period of the light emitting element 20.
An example of an actual detection thereof is given, wherein a detecting device such as a CPU etc. compares the pulse time width light receiving signal with a preset fixed threshold value, and a time width of a light receiving intensity signal over the threshold value is detected from an A/D port. Then, the CPU compares the detected signal time width with a threshold value, stored in a ROM incorporated therein, for judging whether or not the toner is present or not. Then, if the detected signal time width is over a fixed time, the CPU make a judgement of having reached a condition where no toners exist. As a result, an indication of an operator call is given, and the user is notified of this effect through a display etc. on an operation panel (not shown). A relationship between the detected pulse width of the light receiving time signal and the residual toner in the prior art, is as shown in, e.g., FIG. 14.
Incidentally, in the toner residual quantity detecting apparatus of the image of the image forming apparatus, the toners T are, as illustrated in FIG. 15, adhered somewhere along the light path extending from the holder 21 via the light guides 25, 26 to the toner CRG 23 as adhered specifically to the cap portion of the light emitting element 20 or the light receiving element 22 and especially light I/O edge surfaces of the light guides 25, 26, due to a toner leakage from the toner CRG 23 and a change with a passage of time which might be caused by scattering of the toner during an electrophotographic image forming process. Therefore, a light transmittance deceases in inverse proportion to the adhesion of the toner T.
Accordingly, if constructed to detect the light receiving signal with the threshold value fixed as described above, there is a possibility in which almost no toners are left in the toner CRG 23, and nevertheless it might occur that the light signal of the light receiving element 22 is not detected in the worst case. This phenomenon will hereinafter be explained referring to FIG. 16.
As shown in FIG. 16, normally, the light receiving signal exhibiting a light stain condition is still a detection signal under the fixed threshold value (a in FIG. 16 shows the light receiving signal when in the normal condition, and b indicates the light receiving signal when in a light stain condition), and hence the pulse width signal for judging whether or nor the toner is present, is to be generated.
If changed into the light receiving signal (indicated by c in FIG. 16) exhibiting a heavy stain condition due to the change with the passage of time etc, however, the detection signal is never under the fixed threshold value, and therefore the pulse width signal for judging whether or not the toner is present, is not generated.
It might be also considered such a contrivance that a value of the light quantity of the light emitting element or a sensitivity of the light receiving element is increased by previously estimating the stain due to the above-described change made as the time elapses with a conversion from a life-span of the apparatus body. It is, however, difficult to estimate under the worst conditions in terms of a quantity of the toner scattered and leaked. Further, it is impossible to actualize the above contrivance at a stage of mass production in the case of taking into consideration a fitting precision of the light emitting element, the light receiving element and the light guides which constitute the light transmission path, with respect to the optical axis.